Author: Adrian Panella <ianchi74@outlook.com>
Date:   Fri Jun 10 19:10:15 2016 -0500

generic: Mangle bootloader's kernel arguments

The command-line arguments provided by the boot loader will be
appended to a new device tree property: bootloader-args.
If there is a property "append-rootblock" in DT under /chosen
and a root= option in bootloaders command line it will be parsed
and added to DT bootargs with the form: <append-rootblock>XX.
Only command line ATAG will be processed, the rest of the ATAGs
sent by bootloader will be ignored.
This is usefull in dual boot systems, to get the current root partition
without afecting the rest of the system.


Signed-off-by: Adrian Panella <ianchi74@outlook.com>

--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1928,6 +1928,17 @@ config ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEN
 	  The command-line arguments provided by the boot loader will be
 	  appended to the the device tree bootargs property.
 
+config ARM_ATAG_DTB_COMPAT_CMDLINE_MANGLE
+	bool "Append rootblock parsing bootloader's kernel arguments"
+	help
+	  The command-line arguments provided by the boot loader will be
+	  appended to a new device tree property: bootloader-args.
+	  If there is a property "append-rootblock" in DT under /chosen 
+	  and a root= option in bootloaders command line it will be parsed 
+	  and added to DT bootargs with the form: <append-rootblock>XX.
+	  Only command line ATAG will be processed, the rest of the ATAGs
+	  sent by bootloader will be ignored.
+
 endchoice
 
 config CMDLINE
--- a/arch/arm/boot/compressed/atags_to_fdt.c
+++ b/arch/arm/boot/compressed/atags_to_fdt.c
@@ -3,6 +3,8 @@
 
 #if defined(CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND)
 #define do_extend_cmdline 1
+#elif defined(CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_MANGLE)
+#define do_extend_cmdline 1
 #else
 #define do_extend_cmdline 0
 #endif
@@ -66,6 +68,59 @@ static uint32_t get_cell_size(const void
 	return cell_size;
 }
 
+#if defined(CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_MANGLE)
+
+static char *append_rootblock(char *dest, const char *str, int len, void *fdt)
+{
+	char *ptr, *end;
+	char *root="root=";
+	int i, l;
+	const char *rootblock;
+
+	//ARM doesn't have __HAVE_ARCH_STRSTR, so search manually
+	ptr = str - 1;
+
+	do {
+		//first find an 'r' at the begining or after a space
+		do {
+			ptr++;
+			ptr = strchr(ptr, 'r');
+			if(!ptr) return dest;
+
+		} while (ptr != str && *(ptr-1) != ' ');
+
+		//then check for the rest
+		for(i = 1; i <= 4; i++)
+			if(*(ptr+i) != *(root+i)) break;
+
+	} while (i != 5);
+
+	end = strchr(ptr, ' ');
+	end = end ? (end - 1) : (strchr(ptr, 0) - 1);
+
+	//find partition number (assumes format root=/dev/mtdXX | /dev/mtdblockXX | yy:XX )
+	for( i = 0; end >= ptr && *end >= '0' && *end <= '9'; end--, i++);
+	ptr = end + 1;
+
+	/* if append-rootblock property is set use it to append to command line */
+	rootblock = getprop(fdt, "/chosen", "append-rootblock", &l);
+	if(rootblock != NULL) {
+		if(*dest != ' ') {
+			*dest = ' ';
+			dest++;
+			len++;
+		}
+		if (len + l + i <= COMMAND_LINE_SIZE) {
+			memcpy(dest, rootblock, l);
+			dest += l - 1;
+			memcpy(dest, ptr, i);
+			dest += i;
+		}
+	}
+	return dest;
+}
+#endif
+
 static void merge_fdt_bootargs(void *fdt, const char *fdt_cmdline)
 {
 	char cmdline[COMMAND_LINE_SIZE];
@@ -85,12 +140,21 @@ static void merge_fdt_bootargs(void *fdt
 
 	/* and append the ATAG_CMDLINE */
 	if (fdt_cmdline) {
+
+#if defined(CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_MANGLE)
+		//save original bootloader args
+		//and append ubi.mtd with root partition number to current cmdline
+		setprop_string(fdt, "/chosen", "bootloader-args", fdt_cmdline);
+		ptr = append_rootblock(ptr, fdt_cmdline, len, fdt);
+
+#else
 		len = strlen(fdt_cmdline);
 		if (ptr - cmdline + len + 2 < COMMAND_LINE_SIZE) {
 			*ptr++ = ' ';
 			memcpy(ptr, fdt_cmdline, len);
 			ptr += len;
 		}
+#endif
 	}
 	*ptr = '\0';
 
@@ -147,7 +211,9 @@ int atags_to_fdt(void *atag_list, void *
 			else
 				setprop_string(fdt, "/chosen", "bootargs",
 					       atag->u.cmdline.cmdline);
-		} else if (atag->hdr.tag == ATAG_MEM) {
+		}
+#ifndef CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_MANGLE
+		else if (atag->hdr.tag == ATAG_MEM) {
 			if (memcount >= sizeof(mem_reg_property)/4)
 				continue;
 			if (!atag->u.mem.size)
@@ -186,6 +252,10 @@ int atags_to_fdt(void *atag_list, void *
 		setprop(fdt, "/memory", "reg", mem_reg_property,
 			4 * memcount * memsize);
 	}
+#else
+
+	}
+#endif
 
 	return fdt_pack(fdt);
 }
--- a/init/main.c
+++ b/init/main.c
@@ -89,6 +89,10 @@
 #include <asm/sections.h>
 #include <asm/cacheflush.h>
 
+#if defined(CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_MANGLE)
+#include <linux/of.h>
+#endif
+
 static int kernel_init(void *);
 
 extern void init_IRQ(void);
@@ -562,6 +566,18 @@ asmlinkage __visible void __init start_k
 	page_alloc_init();
 
 	pr_notice("Kernel command line: %s\n", boot_command_line);
+
+#if defined(CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_MANGLE)
+	//Show bootloader's original command line for reference
+	if(of_chosen) {
+		const char *prop = of_get_property(of_chosen, "bootloader-args", NULL);
+		if(prop)
+			pr_notice("Bootloader command line (ignored): %s\n", prop);
+		else
+			pr_notice("Bootloader command line not present\n");
+	}
+#endif
+
 	parse_early_param();
 	after_dashes = parse_args("Booting kernel",
 				  static_command_line, __start___param,
